The present invention relates to. a thermoelectric device utilizing, a thermoelectric module utilizable in a refrigerating apparatus and, more particularly to a thermoelectric manifold capable of cooling or heating a thermal medium in a fluid circuit for the thermal medium by utilization of a thermoelectric effect.
In recent years, depletion of the ozone layer in contact with fluorinated hydrocarbon gas has come to be a global problem and immediate development of refrigerating apparatuses that do not use fluorinated hydrocarbons is desired. Also, with the standard refrigerating apparatus utilizing a compressor, noises generated from the compressor are offensive to the ears particularly where the environment in which it is used is quiet. As one of the refrigerating apparatuses that do not use fluorinated hydrocarbons the refrigerating apparatus utilizing a thermoelectric module has now come to be spotlighted.
The Peltier effect is generally well known as a phenomenon in which when a weak electric current flows across the interface between dissimilar metals heat is evolved and absorbed. The thermoelectric module utilizing this Peltier effect is of a design in which pluralities of P-type semiconductor elements and N-type semiconductor elements are arranged in a matrix pattern, having been connected in series with each other through electrodes and are sandwiched between heat transfer plates to render the resultant assembly to represent a generally flat configuration. In this thermoelectric module, when a direct current is applied in one direction to the semiconductor elements, the heat transfer plates are cooled and heated, respectively, by the Peltier effect. Accordingly, one of the heat transfer surfaces acts as an exothermic surface whereas the other of the heat transfer surfaces acts as an endothermic surface.
In the thermoelectric module, it is thought that heat is transported from the endothermic surface towards the exothermic surface by the effect of exchange of kinetic energies and heat energies of electrons flowing through the semiconductor elements. Accordingly, if it is assumed that no heat conduction take place between the heat transfer plates through the semiconductor elements, the difference in temperature between-the endothermic and exothermic surfaces of the single thermoelectric module can be increased by choosing the number of the semiconductor elements and the electric current density.
In reality, however, heat evolved in the heat transfer plate on a heating side transfers to the heat transfer plate on a cooling side as a result of a heat conduction through the semiconductor elements. Accordingly, if the temperature difference between the endothermic and exothermic surfaces of the single thermoelectric module becomes large, the heat capacity brought about upon cooling or heating by the Peltier effect and the heat capacity of the above described heat conduction are counterbalanced with each other and no continued application of an electric current would result in increase of the temperature difference.
Accordingly, in order. for the thermoelectric device having the thermoelectric module built therein to enable the endothermic surface to be cooled down to a desired temperature, the Japanese Laid-open Patent Publication No. 8-236820 discloses stacking of a plurality of thermoelectric module one above the other so that they can be cooled stepwise to thereby enable the endothermic surface on a cooling side to be cooled down to a desired temperature.
With the prior art thermoelectric module, since the pluralities of the P-type semiconductor elements and N-type semiconductor elements are arranged in a matrix pattern and heat transport takes place in each of the semiconductor elements by the Peltier effect, a center portion of the endothermic surface is lower in temperature than that at a peripheral edge portion thereof and, on the other hand, a center portion of the exothermic surface is higher in temperature than that at a peripheral edge portion thereof. If a gradient occurs in a pattern of distribution of temperature at the endothermic surface and also at the exothermic surface, the cooling efficiency exhibited by the endothermic surface as a whole tends to be lowered. In particular, in the thermoelectric refrigerating apparatus utilizing the multi-staged thermoelectric modules, the temperature gradient tends to become large.
Once the temperature gradient becomes large, not only is the heat exchange efficiency reduced, but the thermoelectric module is susceptible to bowing deformation. In such case, cracking may occur at the joint between the semiconductor elements and the electrodes. Also, where a pair of heat transfer plate are used for each of the thermoelectric modules and the heat transfer plates are joined together to allow the plural thermoelectric modules to be laminated, bowing of one or more thermoelectric modules will result in separation of the heat transfer plates from each other and no heat transmission would occur properly between the thermoelectric module.
The present invention has for its object to provide a thermoelectric device such as a thermoelectric manifold having a multi-stage of thermoelectric modules, wherein the heat exchange efficiency is increased by equalizing heat distribution in each of the endothermic and exothermic surfaces and thermal strains in the thermoelectric modules are suppressed so that even though bowing takes place the heat transmission can favorably take place between the thermoelectric modules.
In order to accomplish the above described object, the present invention is such that in the thermoelectric device provided with a plurality of thermoelectric modules, a fluid that serves as a heat transfer medium is intervened between the thermoelectric modules so that through this fluid heat transmission takes place from an exothermic surface of the thermoelectric module on a cooling side towards an endothermic surface of the thermoelectric module on a heating side. Thus, if the heat transmission is caused to occur indirectly between the thermoelectric modules through the fluid, even when thermal strains are induced in the thermoelectric modules, the heat transfer medium favorably contacts the endothermic and exothermic surfaces of the thermoelectric modules with the heat transmission taking place favorably between the thermoelectric modules. Also, heat distribution at the endothermic or exothermic surface of each of the thermoelectric modules held in contact with the fluid can be equalized to thereby increase the heat exchange efficiency and also to lessen the thermal stresses in the thermoelectric modules.
The thermoelectric device of the present invention includes a plurality of thermoelectric modules each having endothermic and exothermic surfaces, wherein when an electric current is supplied the exothermic surface is heated and the endothermic surface is cooled, the plural thermoelectric modules being juxtaposed to each other with the exothermic surface of one of the neighboring thermoelectric modules and the endothermic surface of the other of the neighboring thermoelectric modules being held in face-to-face relation with each other; and a cavity defining member for defining a heat transfer cavity between the neighboring thermoelectric modules.
In the present invention, the fluid that serves as the heat transfer medium is sealed within, or is allowed to flow through, the heat transfer cavity and, by so doing, heat transfer takes place from the exothermic surface of one of the neighboring thermoelectric modules to the endothermic surface of the other of the neighboring thermoelectric modules through this fluid. Accordingly, even-when one or some of the thermoelectric module is deformed to bow under the influence of the thermal strains, the heat transfer medium favorably contacts the exothermic and endothermic surfaces and the heat transfer from the exothermic surface of the thermoelectric module on the cooling side towards the endothermic surface of the thermoelectric module on the heating side takes place favorably, resulting in considerable contribution to increase of the overall efficiency. Also, by the intervention of the heat transfer medium, the heat distribution at the exothermic or endothermic surfaces of each of the thermoelectric module can be equalized, the efficiency of the thermoelectric effect of each of the thermoelectric module can be increased and the thermal strains can be suppressed as small as possible.
The thermoelectric device of the present invention may be provided with a stirring means for stirring the fluid within the heat transfer cavity. According to this, by stirring the fluid within the heat transfer cavity by means of the stirring means, the heat transfer between the thermoelectric modules through the fluid can further efficiently take place. The stirring means achieves the stirring by providing a bypass passage above and below the heat transfer cavity and then by circulating the fluid within the heat transfer cavity by means of a pump, or a stirring blade supported rotatably within the heat transfer cavity may be employed. Also, stirring of the fluid can also be achieved if a plurality of iron balls are movably sealed within the heat transfer cavity and are rotated externally from the outside of the cavity by the action of a magnet.
Where the stirring blade is used for the stirring means, the stirring blade has to be appropriately rotated to achieve stirring of the fluid. As a rotation drive means for the stirring blade, various structures such as an electric motor and a hydraulic motor can be contemplated, but such an arrangement may be employed in which, for example, while a rotor is provided on the stirring blade, a stator which forms an electric motor together with the rotor is provided n the cavity defining member on one side externally of an outer periphery of the stirring blade. According to this, since the rotor is provided on the stirring blade itself, the overall structure can be simplified and compactized and the thermoelectric device of the present invention can be easily installed within a narrow space.
Also, in order to realize a stabilized rotating operation of the stirring blade with a simplified structure, the stirring blade may be rotatably supported by a support shaft which is in turn supported by an oscillation preventing member held in abutment with an inner surface of the heat transfer cavity defining member. It is to be noted that such an oscillation preventing member may be of a flat shape and preferably of a type contacting at least three locations of the inner surface of the heat transfer cavity, and is preferably constructed from a generally cross-shaped flat plate.
In order that in the above described thermoelectric device provided with the multi-staged thermoelectric modules the temperature difference between the endothermic and exothermic surfaces of each of the thermoelectric module can be optimized and the thermoelectric efficiency can further be increased, the thermoelectric modules may have different powers. In other words, where each of the thermoelectric module comprises the Peltier element provided with the P-type and N-type semiconductors connected in series with each other, the number of the semiconductors forming the respective thermoelectric module may differ from one thermoelectric module to another so that the powers of those thermoelectric modules can be adjusted. Also, even where a number of the same thermoelectric modules are employed, application of the electric current of a density different for each of the thermoelectric module is effective to differentiate the thermoelectric powers of the thermoelectric modules during operation.
Furthermore, arrangement may be made in which of the juxtaposed thermoelectric modules the thermoelectric modules on one side adjacent a cooling end may be provided with the cavity defining member for defining a cooling cavity between the endothermic surfaces thereof, which cavity defining member may be provided with an fluid inlet and a fluid outlet. According to this, the fluid introduced from the fluid inlet in the cooling cavity defining member into the cooling cavity can be caused to contact the endothermic surfaces on the side adjacent the cooling end to cool efficiently and can subsequently be discharged through the fluid outlet. If the fluid outlet is coupled with a heat exchanger such as, for example, that of a refrigerator, a desired space can be efficiently cooled through the fluid. Also, since the thermoelectric modules are arranged in multiple stages, as compared with a single stage a low temperature can easily be obtained and a desired temperature can be obtained even though compact and low in noise.
Also, arrangement may be made in which of the juxtaposed thermoelectric modules the thermoelectric modules on one side adjacent a heating end may be provided with the cavity defining member for defining a heating cavity between the exothermic surfaces thereof, which cavity defining member may be provided with a fluid inlet and a fluid outlet. According to this, the fluid introduced from the fluid inlet in the heating cavity defining member into the heating cavity can be caused to contact the exothermic surfaces on the side adjacent the heating end to efficiently cause heat evolved by the thermoelectric modules to be dissipated to the fluid and can subsequently be discharged through the fluid outlet. If the fluid outlet and the fluid inlet are coupled with an external heat discharge piping, the fluid serving as the heated heat transfer medium can be efficiently cooled naturally for reuse and the temperature at the endothermic surfaces on the side adjacent the cooling end can further be reduced down to a lower temperature.
Also, arrangement may be made in which of the juxtaposed thermoelectric modules the thermoelectric modules on one side adjacent a heating end may be provided with the cavity defining member for defining a heating cavity between the exothermic surfaces thereof, which cavity defining member may be provided with a fluid inlet and a fluid outlet. According to this, the fluid introduced from the fluid inlet in the heating cavity defining member into the heating cavity can be caused to contact the exothermic surfaces on the side adjacent the heating end to efficiently cause heat evolved by the thermoelectric modules to be dissipated to the fluid and can subsequently be discharged through the fluid outlet. If the fluid outlet and the fluid inlet are coupled with an external heat discharge piping, the fluid serving as the heated heat transfer medium can be efficiently cooled naturally for reuse and the temperature at the endothermic surfaces on the side adjacent the cooling end can further be reduced down to a lower temperature.
The above described thermoelectric device can be employed in various applications and in various embodiments. By way of example, it can be used as a cooling device such as a refrigerator or a cooler. Also, it can be built in a manifold which provides a flow tube for the heat transfer medium on the cooling side and/or the heat transfer medium on the heating side in, for example, a refrigerator so that cooling or heating of the heat transfer medium can be performed within the flow tube.
The present invention can be realized as a thermoelectric manifold having the thermoelectric module built in the manifold. In such thermoelectric manifold of the present invention, there is provided a plurality of thermoelectric modules each having endothermic and exothermic surfaces in which when an electric current is supplied the exothermic surface is heated and the endothermic surface is cooled, the plural thermoelectric modules being juxtaposed within a manifold body with the exothermic surface of one of the neighboring thermoelectric modules facing the endothermic surface of the other of the neighboring thermoelectric modules, a cooling cavity being provided within the manifold body and between the endothermic surfaces on one side adjacent the cooling end while a heating cavity is provided between the exothermic surfaces on one side adjacent the heating end, a heat transfer cavity being provided between the neighboring thermoelectric modules.
In the thermoelectric manifold of the present invention, a fluid serving as a cooled heat transfer medium is supplied into the cooling cavity whereas a fluid serving as a heated heat transfer medium is supplied into the heating cavity, and a fluid serving as a heat conducting heat transfer medium is sealed within or supplied into the heat transfer cavity, and a direct current is supplied to the thermoelectric module in a predetermined direction. Thereupon, not only is the cooled heat transfer medium contacting the endothermic surfaces on the side adjacent the cooling end is cooled, but the heated heat transfer medium contacting the exothermic surfaces on the side adjacent the heating end is heated. Also, heat transfer between the thermoelectric modules is carried by the fluid within the heat transfer cavity. Since the heat transfer is carried out between the thermoelectric modules through the fluid, even when the thermoelectric modules are deformed to bow under the influence of thermal strains, there is no possibility that the efficiency of heat transmission between the thermoelectric modules will decrease considerably. Accordingly, movement of heat from the cooled heat transfer medium towards the heated heat transfer medium takes place efficiently and the cooled heat transfer medium can be cooled down to a desired low temperature.
In the above described thermoelectric manifold of the present invention, the cooling cavity, the heating cavity and the heat transfer cavity may have respective stirring members disposed therein for stirring the fluids within such cavities. According to this, by stirring the fluids within each of those cavities by means of the associated stirring member, the fluid within the cooling cavity can be efficiently cooled, a highly efficient heat transfer can take place within the heat transfer cavity, and the heat can be dissipated efficiently to the fluid within the heating cavity.
Although the stirring members can be driven by respective drive means, in order to simplify the structure, to reduce the number of component parts and to render the device to be compact, they are preferably associate with each other by the utilization of magnetism. In other words, it is possible to arrange the endothermic and exothermic surfaces of the thermoelectric modules so as to be parallel to each other, to cause the stirring members to be supported rotatably within the manifold body for rotation about respective axes perpendicular to any one of the endothermic and exothermic surfaces and then to provide a paramagnetic body on each of the stirring member so that those stirring member can be driven in association with each other. It is to be noted that the number of paramagnetic bodies provided on each of the stirring members is preferred to be sufficient to transmit a rotational force, but all of them need not be a paramagnetic body and soft magnetic bodies such as iron can be appropriately provided.
Where the paramagnetic bodies are provided as rotational force transmitting means for the stirring members, if a rotational drive means is provided for the stirring member within one of the cooling cavity, the heating cavity and the heat transfer cavity, all of the stirring members can be driven. Such a rotational drive means may be of a type provided, for example, with a rotor provided on the stirring member within the cooling cavity or the heating cavity, and a stator provided on the manifold body and constitute an electric motor in cooperation with the rotor.
Also, even if the stator for- driving the stirring member with the paramagnetic bodies provided on the stirring member used as the rotor is provided radially outwardly of the stirring member within at least one heat transfer cavity, the rotational drive means for the stirring members can be constituted. According to this, since the stirring member at an intermediate position is driven and the rotational force produced thereby is transmitted to the stirring members on the heating and cooling sides, respectively, a loss of the rotational force is small and a highly efficient rotation can be achieved.
Also, in order to realize a stable rotation of the stirring member within the heat transfer cavity with a simplified structure, the stirring member may be rotatably supported by a support shaft which is in turn supported by an oscillation preventing member positioned in the manifold body. It is to be noted that such oscillation preventing member may be of a flat shape and preferably of a type contacting at least three locations of the inner surface of the heat transfer cavity, and is preferably constructed from a generally cross-shaped flat plate.
Also, in order that in the thermoelectric manifold provided with the multi-staged thermoelectric modules the temperature difference between the endothermic and exothermic surfaces of each of the thermoelectric module can be optimized and the thermoelectric efficiency can further be increased, the thermoelectric modules may have different powers. In other words, where each of the thermoelectric module comprises the Peltier element provided with the P-type and N-type semiconductors connected in series with each other, the number of the semiconductors forming the respective thermoelectric module may differ from one thermoelectric module to another so that the powers of those thermoelectric modules can be adjusted.